Mast snubber



July 11, 1967 R. J. PUSZTAY MAST SNUBBER Filed March 28, 1966 UnitedStates Patent O 3,330,383 MAST SNUBBER Russell J. Pusztay, Dalton, Ill.,assigner to Allis-Chalmers Manufacturing Company, Milwaukee, Wis. FiledMar. 28, 1966, Ser. No. 537,869 Claims. (Cl. 187-9) This inventionrelates to means for retarding the free fall of the inner section of anextra lift mast.

In a typical extra lift mast the crosshead of the lift cylinder has alost motion connection with the inner section of the mast and thus doesnot pick up the inner section of the mast until the carriage has beenraised a predetermined distance from the oor. This initial movement ofthe carriage does not increase the height of the mast assembly and iscommonly referred to as free lift. At the upper end of the lift ramstroke the carriage will lift the inner section of the mast off thecrosshead. When the mast is retracted from such a fully extendedposition the weight of the inner section may be insufficient to overcomebinding or friction lbetween the inner and outer mast sections. Whenthis occurs, the crosshead will move downwardly through a part or all ofits lost motion connection with the inner section before the binding orfriction is overcome. When the inner section is freed it will drop bygravity onto the lift ram crosshead. This dropping of the inner sectionof the mast not only imposes shock load on various components, but alsothe sound of impact is annoying and distracting to the operator andpersonnel in the vicinity of lift truck use.

Heretofore others have employed latches to positively effect propercycling of the mast components; however, such mechanisms are costly anddo not have satisfactory service life.

It is an object of this invention to reduce the speed and force of thedrop of the inner mast section relative to the lift cylinder crosshead.

It is a further object to provide a snubbing mechanism to retard thedescent of an inner mast section when dropping by gravity.

It is a further object of this invention to provide a snubber orretarder for an inner mast section which is adjustable and automatic inoperation.

It is a further object of this invention to provide a mast snubber ofthe nature hereinbefore outlined which is economical to manufacture,easy to install and service and reliable in operation.

These and other objects and advantages of this invention will beapparent when the following description is read in conjunction with thedrawings in which:

FIG. 1 is a rear view of a mast assembly for a lift truck in which thepresent invention is incorporated;

FIG. 2 is a top view of the mast assembly of FIG. l;

FIG. 3 is a section view taken along the line III-III of FIG. 1;

FIG. 4 is a section view of the mast snubbing mechanism of thisinvention;

FIG. 5 is a section view taken along the line V-V of FIG. 4; and

FIGS. 6, 7 and 8 are section views showing the mast and carriage indifferent positions of operation.

The mast assembly illustrated in the drawings includes an outer section11 adapted for connection to the body of a lift truck through pivotbrackets 12, 13, 14, 1S and an inner section 16 telescopically mountedfor vertical reciprocable movement on the outer mast section 11. Themast assembly also includes a carriage 17, lift ram 18 and chains 19interconnecting the ram and carriage. A piston 21 of ram 18 has aportion extending out of the top of the ram cylinder 22 which carries acrosshead 23 with sprockets 24 over which chains 19 are reeved. The

3,336,383 Patented July 11, 1967 ICC carriage moves up and down thechannel members 26, 27 of the inner section 16 of the mast assembly onfour spaced rollers 28 journaled on the back of the carriage. A pair ofguide rods 31, welded to struts 32, 35 of the inner section 16, maintainthe ram 18 in a vertical attitude by a sliding, loose tit connectionwith vertical openings 30 in crosshead 23, thus providing a lost motionconnection between the crosshead 23 and inner mast section 16.

When the ram is expanded the piston 21 and its crosshead 23 moveupwardly causing the carriage 17 to be raised. When the crosshead 23abuts the underside of strut 32 welded to the upper ends of channels 26,27, it will pick up the inner mast section .16 upon further expansion orextension of the lift ram 18 as shown in FIG. 6. During furtherextension of the ram, the rearwardly extending roller supports 33, 34 ofthe carriage will pick up the inner section 16 as shown in FIG. 7 andcarry it to the upper extreme of its lost motion connection with thecrosshead.

Occasionally the inner mast section 16 will bind with the outer mastsection 11 causing it to hang up during lowering of the carriage andwhen the ram is retracted the inner section 16 will not follow thecarriage roller `supports 33, 34 or crosshead 23 as it should for aproper cycling sequence. FIG. 8 shows the inner mast section 16 hung up,with the carriage 17 and crosshead 23 lowered from their uppermostpositions. As the ram piston 21 is retracted further, the crosshead 23will reach the lower extreme of its lost motion connection with theinner mast section 16 and the latter will be pulled down overcoming thefrictional forces causing it to hang up. Heretofore, on miscycling, theinner section 16 would drop by gravity, when freed, through a portion ofthe lost motion distance with the strut 32 banging against the top ofthe crosshead 23 with a loud irritating noise and with considerableattending shock load.

In order to reduce the speed of the falling inner section 16, I providea snubber mechanism 41 which is secured by cap screw 42 to the undersideof the cro-sshead 23. The snubber mechanism 41 includes a body part orblock 43 having a pair of conical bores 45 which are coaxial to the axesof rods 31, respectively.

As shown in FIGS. 4 and 5 the block 43 is adjustably spaced from thecrosshead 23 by shim means in the form of washers 44. A frictional dragis imposed on each rod by three wedging elements or segments 46 whichare i biased toward their position of greatest wedging eiect tby a wavespring 47. The biasing eifect of the wave spring 47 may be adjusted byadding or removing one or more Washers 44. When the inner mast section16 and its guide rods 31 move upwardly relative to the crosshead 23, thewedging segments 46 tend to shift upwardly against the biasing action ofspring 47 thereby decreasing the frictional drag on the rods 31.However, when the inner section 16 moves downwardly relative to thecrosshead 23, the frictional engagement between the inner cylindricalsurfaces of the segments 46 and the rods tend to shift the lsegmentsdownwardly and the outer conical surfaces of the segments cam againstthe surface of conical bore 45 to apply increased radial thrust againstthe rod 31, thereby increasing resistance to downward movement of theinner section 16 relative to the crosshead 23. Thus the -snubbermechanism acts as a one-way friction device to reduce the speed andimpact force of a free falling inner mast section.

The conical surfaces of the tapered bores 45 and the segments 46 arepreferably coated with a dry lubricant, which may be baked on or airdried, to insure proper operation. The angle of the taper bore may bechanged to suit the requirements of the weight of the inner mast sectionand the amount of braking force desired.

The embodiments of the invention for which an exclusive property orprivilege is claimed are defined as follows: Y

1. In a lift truck mast assembly, the combination cornprising:

a vertically Vdisposed lift ram having a vertically `reciprocable headstructure,

a vertically reciprocable mast section structure,

connecting means interconnecting said structures for a predeterminedamount of vertical lost motion, and

a mechanical snubbing mechanism secured to one of said structures andfrictionally engaging the other of said structures to retard downwardmovement of said mast section structure relative to said head structure,said mechanism affording markedly less resistance to upward movement ofsaid mast section structure relative to said head structure than to saiddownward movement.

2. The `combination of claim 1 wherein said snubbing mechanism includesa spring loaded tapered Wedging element.

3. The combination of claim 2 wherein said one strucing through whichVsaid rod concentrically extends, aVV

plurality of tapered wedging elements in said tapered opening engagingsaid rod and spring means biasing saidV tapered wedging elements towardincreased frictional engagement with said rod.

5. The combination of claim 4 wherein said snubbing mechanism includesmeans for adjusting the biasing effect of said spring means.

References Cited UNITED STATES PATENTS 3,231,047 l/l966 Quayle r 187-'9FOREIGN PATENTS 1,071,064 lll/1954 France.

EVON C. BLUNK, Primary Examiner. H. C. HORNSBY, Assismm Examiner.

1. IN A LIFT TRUCK MAST ASSEMBLY, THE COMBINATION COMPRISING: AVERTICALLY DISPOSED LIFT RAM HAVING A VERTICALLY RECIPROCABLE HEADSTRUCTURE, A VERTICALLY RECIPROCABLE MAST SECTION STRUCTURE, CONNECTINGMEANS INTERCONNECTING SAID STRUCTURES FOR A PREDETERMINED AMOUNT OFVERTICAL LOST MOTION, AND A MECHANICAL SNUBBING MECHANISM SECURED TO ONEOF SAID STRUCTURES AND FRICTIONALLY ENGAGING THE OTHER OF SAIDSTRUCTURES TO RETARD DOWNWARD MOVEMENT OF SAID MAST SECTION STRUCTURERELATIVE TO SAID HEAD